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- Dangles
- ---------
- GRASS doesn't allow areas/islands with dangles. If an island has dangle, it is not built
- and attached to outer area and as a consequence, some functions do not work as expected.
- For example Vect_area_area() and Vect_find_area().
- See comments in build_nat.c: Vect_attach_centroids()
- Category index
- ----------------
- Category index is created when Vect_build(), i.e. Vect_build_partial(, GV_BUILD_ALL,)
- is called. Plus_head.cidx_up_to_date is set to 1 if Category index is created.
- Any later call to Vect_write_line() / Vect_rewrite_line() / Vect_delete_line() resets
- Plus_head.cidx_up_to_date to 0 and doesn't update category index.
- All modules using update on level 2 must call full build, i.e. Vect_build(), at the end.
- All features without category are written to category index of field 0.
- The category index also stores type of feature, that makes it possible to find areas
- without centroid through category index.
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